1. Field of the Invention
The present invention relates to a printer, facsimile apparatus, multifunction machine or similar image forming apparatus. More particularly, the present invention relates to a process cartridge and a device unit removably mounted on an image forming apparatus and a packed kit of the same.
2. Description of the Background Art
It is a common practice with a color copier or similar color image forming apparatus to removably mount a plurality of process cartridges each being assigned to yellow, magenta, cyan or black toner on the apparatus body. The process cartridges each are replaced with new one when, e.g., its mechanical life ends. More specifically, before four new process cartridges are mounted to an image forming apparatus, their developing devices each are filled with a developer containing one of yellow toner, magenta toner, cyan toner and black toner, i.e., either one of a one-ingredient type developer and a two-ingredient type developer. Subsequently, such new process cartridges each are mounted to a particular mount portion included in the new image forming apparatus. Subsequently, when the life of a photoconductive drum or image carrier, developer or similar component of any one of the process cartridge ends due to repeated operation of the apparatus, the user of the apparatus or a service person removes the process cartridge from the apparatus body and then mounts a new process cartridge to the apparatus body.
The prerequisite with the image forming apparatus thus loaded with a plurality of removable process cartridges is that each process cartridge be correctly mounted to preselected one of the mount portions of the apparatus, i.e., a process cartridge assigned to one color be prevented from being mounted to a mount portion assigned to another color. Japanese Patent Laid-Open Publication No. 2003-84543, for example, proposes to provide four process cartridges each having a particular configuration and four mount portions respectively matching in configuration with the process cartridges, thereby obviating erroneous replacement.
However, the problem with the conventional image forming apparatus described above is that the process cartridges need high production cost and moreover need high inventory control cost when stocked. More specifically, the user of the color image forming apparatus of the type described suitably replaces four different kinds of process cartridges that are not replaceable with each other. Therefore, the manufacturer or the distributor of such image forming apparatuses are required to constantly store new process cartridges for replacement as a stock for meeting users' urgent requests. Stocking four different kinds of process cartridges at all times is inefficient from the standpoint of cost and labor for inventory control.
In light of the above, a full-color process cartridge, supporting four different process cartridges assigned to one color each, has been proposed in the past. However, such a process cartridge is naturally bulky and obstructs efficient replacement of the process cartridges while being undesirable from the inventory control standpoint. Further, when the life of one of the four process cartridges ends, even the other process cartridges must be wastefully replaced despite that they are still usable. Moreover, the four process cartridges different in configuration from each other must be produced independently of each other, so that the number of parts and the number of assembling steps increase with the result that the production cost increases.
The problems stated above are not particular to an image forming apparatus of the type using a plurality of process cartridges, but also arise with, e.g., an image forming apparatus in which a plurality of developing units, each including a developing device, are removably mounted to an apparatus body.